Organo-silsesquioxane polymers for forming low-k dielectrics

ABSTRACT

A low dielectric constant polymer, comprising monomeric units derived from a compound having the general formula I (R 1 —R 2 ) n —Si—(X 1 ) 4-n , wherein each X 1  is independently selected from hydrogen and inorganic leaving groups, R 2  is an optional group and comprises an alkylene having 1 to 6 carbon atoms or an arylene, R 1  is a polycycloalkyl group and n is an integer 1 to 3. The polymer has excellent electrical and mechanical properties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to hybrid silsesquioxane polymers suitableas low-k dielectrics in integrated circuits (IC's) and for other similarapplications. In particular, the invention concerns a composition andprocessing method for thin films comprising polymer compositions oforganic-inorganic hybrid materials.

2. Description of Related Art

Built on semiconducting substrates, integrated circuits comprisemillions of transistors and other devices, which communicateelectrically with one another and with outside packaging materialsthrough multiple levels of vertical and horizontal wiring embedded in adielectric material. Within the multilayer metallization structure,“vias” make up the vertical wiring, whereas “interconnects” form thehorizontal wiring. Fabricating the metallization can involve thesuccessive depositing and patterning of multiple layers of dielectricand metal to achieve electrical connection among transistors and tooutside packaging material. The patterning for a given layer is oftenperformed by a multi-step process comprising layer deposition,photoresist spin, photoresist exposure, photoresist develop, layer etch,and photoresist removal on a substrate. Alternatively, the metal maysometimes be patterned by first etching patterns into a layer of adielectric material, filling the pattern with metal, then subsequentlychemically/mechanically polishing the metal so that the metal remainsembedded only in the openings of the dielectric. As an interconnectmaterial, aluminum has been utilized for many years due to its highconductivity, good adhesion to SiO₂, known processing methods(sputtering and etching) and low cost. Aluminum alloys have also beendeveloped over the years to improve the melting point, diffusion,electromigration and other qualities as compared to pure aluminum.Spanning successive layers of aluminum, tungsten has traditionallyserved as the conductive via plug material.

In IC's, silicon dioxide, having a dielectric constant of around 4.0,has been the dielectric of choice, used in conjunction withaluminum-based and tungsten-based interconnects and via for many years.

The drive to faster microprocessors and more powerful electronic devicesin recent years has resulted in very high circuit densities and fasteroperating speeds which—in turn—have required that higher conductivitymetals and lower-k dielectrics (preferably below 3.0, more preferablybelow 2.5 dielectric constant) be used. In the past few years, VLSI (andULSI) processes have been moving to copper damascene processes, wherecopper (or a copper alloy) is used for the higher conductance in theconductor lines and a spin-on or CVD process is used for producing low-kdielectrics which can be employed for the insulating materialsurrounding the conductor lines. To circumvent problems with etching,copper along with a barrier metal is blanket deposited over recesseddielectric structures consisting of interconnect and via openings andsubsequently polished in a processing method known as the “dualdamascene.” The bottom of the via opening is usually the top of aninterconnect from the previous metal layer or, in some instances, thecontacting layer to the substrate.

In addition to being lithographically patternable, the dielectric ICmaterial should be easy to deposit or form, preferably at a highdeposition rate and at a relatively low temperature. Once the materialhas been deposited or formed, it should also be readily patterned, andpreferably patterned with small feature sizes if needed. The patternedmaterial should preferably have low surface and/or sidewall roughness.It might also be desirable that such materials be hydrophobic to limituptake of moisture (or other fluids), and be stable with a relativelyhigh glass transition temperature (not degrade or otherwise physicallyand/or chemically change upon further processing or when in use).

Summarizing: aside from possessing a low dielectric constant, the idealdielectric should have the following properties:

1. High modulus and hardness in order to bind the maze of metalinterconnects and vias together as well as abet chemical mechanicalpolishing processing steps.

2. Low thermal expansion, typically less than or equal to that of metalinterconnects.

3. Excellent thermal stability, generally in excess of 400° C.

4. No cracking, excellent fill and planarization properties

5. Excellent adhesion to dielectric, semiconductor, and metal materials.

6. Sufficient thermal conductivity to dissipate joule heating frominterconnects and vias.

7. Material density that precludes absorption of solvents, moisture, orreactive gasses.

8. Allows desired etch profiles at very small dimensions.

9. Low current leakage, high breakdown voltages, and low loss-tangents.

10. Stable interfaces between the dielectric and contacting materials.

By necessity, low-k materials are usually engineered on the basis ofcompromises. Silicate-based low-k materials can demonstrate exceptionalthermal stability and usable modulus but can be plagued by brittlenessand cracking. Organic materials; by contrast, often show improvedmaterial toughness, but at the expense of increased softness, lowerthermal stability, and higher thermal expansion coefficients.

Porous materials sacrifice mechanical properties and possess a strongtendency of absorbing chemicals used in semiconductor fabricationleading to reliability failures. Furthermore, these porous materials aremesoporous or micro porous with pore diameters in excess of 2 nm andpore volumes greater than 30%. Fluorinated materials can inducecorrosion of metal interconnects, rendering a chip inoperative.Generally, the mechanical robustness and thermal conductivity of low-kmaterials is lower than the corresponding properties of their puresilicon dioxide analogues, making integration into the fabrication flowvery challenging.

Further, known materials comprising exclusively inorganic bonds makingup the siloxane matrix are brittle and have poor elasticity at hightemperatures.

Organosiloxane materials are typically deposited via spin-on processing,however Chemical Vapor Deposition (CVD) is also a viable technique forthe deposition of these materials. For example, published InternationalPatent Application No. WO03/015129 discloses organosilicone low-kdielectric precursors, which are useful for producing porous, low-kdielectric, SiOC thin films, wherein the organosilicon precursorcomprises at least one cleavable, organic functional group that, uponactivation, rearranges, decomposes and/or is cleaved-off as a highlyvolatile liquid and/or gaseous by-product. Other organosiliconeprecursors comprising Si—O—C-in-ring cyclic siloxane compounds for useas precursors for forming insulator films by CVD are described in U.S.Pat. No. 6,440,876. When these siloxane precursors are contacted withthe surface of a semiconductor or integrated circuit, they will reactwith the wafer surface forming a dielectric film. By ring-openingpolymerization of these cyclic compounds, a dielectric film or layerwill be formed.

U.S. Pat. No. 6,242,339 discloses an interconnection structure, in whicha phenyl group, bonded to a silicon atom, is introduced into the silicondioxide of the organic-containing silicon dioxide to produce a materialsuitable as an interlevel insulating film. Such a film can be processedjust as easily as a conventional CVD oxide film; it has a relativedielectric constant as low as that of a hydrogen silsesquioxane (HSQ)film, and can adhere strongly to an organic film, an oxide film or ametal film. According to the patent, the number of devices that can beintegrated within a single semiconductor integrated circuit can beincreased without modification of the conventional semiconductor devicemanufacturing process to provide a high-performance semiconductorintegrated circuit, operative at high speed and with lower powerdissipation.

On the other hand, there are several examples of organosiloxane low-kmaterials made by spin-on deposition techniques. Spin-on low-k materialsknown in the prior art are mainly based on methyl- or phenyl-substitutedorganosiloxanes and combinations thereof. There are also some examplesof adamantyl-substituted organosiloxanes.

The use of these types of polymers results, however, in fundamentalproblem due to their polarizability nature. The methyl-based siloxanes(also known as silsesquioxanes) will give relatively low electronicdielectric constant (polarizability), more specifically approximately1.88, but—by contrast—their orientational dielectric constant(polarizability) is high, i.e., approximately 0.7, which significantlyincreases the total dielectric constant measured at low frequencies (10kHz-10 GHz). Again, phenyl-based organosiloxanes have higher electronicdielectric constant (polarizability), i.e., approximately 2.4, but theirorientational dielectric constant (polarizability) is lower(approximately 0.4) due to a relatively lower content of permanentdipoles in the material matrix. Therefore, the total dielectric constantcannot reach values close to 2.5 or lower, when ionic dielectricconstant (polarizability) of approximately 0.15-0.3 is included, withoutthe introduction of porosity (air having a dielectric constant of 1)into the film matrix. Moreover, the porous materials that are currentlyreaching a dielectric constant of less than 2.5 are typically highlyporous, which makes the integration of such materials into thesemiconductor device very difficult.

A particular problem with the adamantyl-substituted siloxanes known inthe art is that they have been produced from alkoxy-precursors, whichleave alkoxide residues in the matrix of the material. Such residuesgreatly impair the use and properties of the materials in particular asregards their dielectric properties. If residual alkoxides remain in thematrix, they tend to react over time and change materials properties byforming contaminating alcohol and water into the matrix. Such oxygenatesdecrease dielectric and leakage current behavior of the material. Inaddition, residual alkoxides, such as ethoxide-based materials, cause adangling bond effect that causes higher leakage current for thematerial. Further, there are no industrially viable processes forproducing suitable adamanlyl-substituted siloxane precursors.

Thus, the prior art contains no examples of dielectric materials forsemi-conductor manufacture, which have desired properties of lowdielectric constant with low controlled micro porosity, high thermalstability, and low cost. Further, there is a need for new precursors forhybrid organo-silsequioxane polymers.

SUMMARY OF THE INVENTION

It is an aim of the present invention to eliminate disadvantages of theprior art and to improve the dielectric constant performance oforganosiloxane material compositions by providing novel polymer films,which have a low dielectric constant and excellent mechanical andthermal properties.

It is a second object of the invention to provide methods of producingnovel poly(organo siloxane) compositions, which are suitable for thepreparation of thin films having low dielectric constant.

Materials providing dielectric constant values of <2.5 and even <2.3 arealso claimed.

It is a third object of the invention to provide a method of processingthe new materials polymers by spin-on deposition methods.

A fourth object of the invention is to provide a method of processingthe new materials by Chemical Vapor Deposition (CVD) methods.

Still, a fifth object of the invention is to apply above mentionedprecursor and polymers in a rapid thermal anneal process whereindielectric constant is further reduced.

These and other objects, together with the advantages thereof over theknown dielectric thin films and methods for the preparation thereof,which shall become apparent from specification which follows, areaccomplished by the invention as hereinafter described and claimed.

The present invention is based on the finding that by incorporating alarge portion of an organic moiety into a hybrid organo-silsequioxanepolymer, novel low dielectric constant polymer films having excellentmechanical and thermal properties can be obtained. Such materials arepreferably produced from polycycloalkyl-substituted siloxanes, inparticular from polycycloalkyl-substituted siloxanes, which aresubstantially free of any oxygenate impurities that may impair thedielectric properties of the dielectric material.

Polycycloalkyl siloxane precusors used according to the invention forproducing dielectric polymer are typically compounds, which comprise anorganic moiety, formed by at least two rings. Preferably the organicmoiety comprises a plurality of rings, e.g. three or more aliphaticrings, formed by covalently bound atoms, which define a volume. Suchcompounds can be called “cage” compounds in the sense that a straightline draw between any point within the volume to any point outside thecompound will always pass through one ring of the molecule. Theprecursors comprise an inorganic moiety formed by a silicon atom, whichis bound to the organic moiety either directly or indirectly through alinker compound. Further the silicon atom bears at least one cleavableinorganic substituent, which will form a leaving group when theprecursor is polymerized, or a proton. The substituent can be cleaved,in particular, by hydrolysis.

According to a preferred embodiment, the precursor has the generalformula I(R¹—R²)_(n—Si—(X) ¹)_(4-n),wherein

-   -   each X₁ is independently selected from hydrogen and inorganic        leaving groups,    -   R₂ is an optional group and comprises alkylene having 1 to 6        carbon atoms or arylene,    -   R₁ is a polycycloalkyl group and    -   n is an integer 1 to 3

Of the above compounds, adamantyl trihalosiloxane and adamantyl silaneare particularly interesting because they can now be economicallyproduced at high yield and purity by a novel chemical process involvingas a key intermediate adamantyl dehydrate having the formula

Specific preferred compounds include the following: adamantyltrichlorosilane, adamantylpropyl trichlorosilane,3,5,7-trifluoroadamantyl trichlorosilane, 3,5,7-trifluoromethyladamantyltrichlorosilane and adamantylphenyl trichlorosilane.

The invention is also based on the finding that using polymers, whichcomprise organic residues derived from the above-describedpolycycloalkyl-substituted siloxanes in combination with residuesderived from conventional precursors of dielectric polymers, such asalkyl-, aryl- and/or vinyl-substituted siloxanes, novel compositematerials having excellent mechanical and dielectrical properties areproduced. The properties of the composites are, in fact, better thanthose provided for by either of the homopolymers as such.

More specifically, the invention is mainly characterized by what isstated in the characterizing parts of claims 1, 22, 45 and 47.

Considerable advantages are achieved by the invention. Thus, nonporousmaterials having a porosity volume of less than 25% and a pore radius ofapproximately 1 nm or less, can be produced. These materials have arelative dielectric constant of less than 2.6 and high elasticity(Young's modulus 4 GPa or higher). By using polycycloalkyl siloxanes ascomonomers together with conventionally used alkyl, vinyl and/or arylsiloxanes in the preparation of hybrid organo-silsequioxane polymers, itis possible to produce materials having a desired combination ofelectrical and mechanical properties.

Next, the invention will be examined in more detail with the help of adetailed description and with reference to the attached drawing and anumber of chemical working examples.

DETAILED DESCRIPTION OF THE INVENTION

The present innovation relates to organosiloxane precursor and polymers,whose orientational and electronic polarizabilities result in a lowertotal dielectric constant than know in the prior art. Especially, theinnovation relates to the use of organo-rich moieties that reduces therelative content of permanent dipoles in the film of the formed filmmatrix. In siloxane, the permanent dipoles of the polymers are mainlydue to oxygen atoms in Si—O—Si bridges. When silane precursorscontaining polycyclic alkyl moieties are used for the formation ofsiloxane polymers, the organic content of the film is increased and,therefore, the content of carbon related oxygen is significantly reducedcompared to siloxane polymers formed from precurors containing smallalkyl groups. Examples of the latter kind of precursors are themethyl-substituted siloxanes. By “polycyclic alkyl moiety” we mean, forexample, an adamantyl group or a similar cage compound, which isattached to silicon by (at least one) covalent bond. Thus, for example,if each silicon atom in the deposition polymer matrix contains onerelative large organic group, in case of adamantyl, the atomic ratio ofcarbon to oxygen is increased. Thus, a conventional siloxane polymercontains significantly more permanent dipoles than a siloxane polymermade of adamantyl containing precursors. This difference in the contentof permanent dipoles affects orientational polarizability so that theorientational dielectric constant can be as low as 0.3 to 0.2 for thesiloxane materials made of adamantyl substituted precursors whereas anorientational dielectric constant for conventional siloxane low-kmaterial is typically 0.7 or higher.

On the other hand, higher carbon content materials have a tendency ofyielding a higher electronic polarizability especially when carbon isnon-fluorinated carbon. Therefore, for example, an adamantyl siloxanepolymer, in which each silicon atom contains one adamantyl group, givesan electronic dielectric constant of 2.25, whereas a similar polymerhaving a methyl group attached to the silicon instead results in anelectronic dielectric constant of 1.89, provided that both of thematerials are fully dense.

Thus, it is important in course of innovation to use compositions inwhich the sum of electronic and orientational polarizabilities isminimized.

Therefore, according to one preferred embodiment of the presentinvention, organosiloxane polymers made of adamantyl and methyl residuescontaining precursors at specific molar ratios are provided. Sixcompositional examples including their electronic dielectric,orientational dielectric and total dielectric constants with variableadamantyl and methyl concentrations in the organosiloxane polymer arereported in Table 1. The material compositions are presented in molarratios as in the deposition polymer stage. All compositions have anintramolecular porosity of approximately 15%. TABLE 1 ElectronicOrientational Total Organic Carbon Oxygen Material k k k content (wt-%)content (at-%) content (at-%) 100 adamantyl - 0 methyl 1.92 0.31 2.4372.2 36.4 5.5 75 adamantyl - 25 methyl 1.86 0.335 2.4 66.9 34.8 6.7 50adamantyl - 50 methyl 1.8 0.37 2.37 59.1 32.4 8.8 30 adamantyl - 70methyl 1.78 0.35 2.33 49.5 28.9 11.7 25 adamantyl - 75 methyl 1.74 0.432.37 46.4 27.7 12.8 0 adamantyl - 100 methyl 1.68 0.55 2.43 22.4 15.423.1

As will appear from the table, particularly good results are obtainedwhen the organic content is in the range of 30 to 70 wt.-%, preferablyabout 40 to 60 wt.-%.

Similar results are obtained when polycyclic alkyl siloxanes are used ascomonomers in combination with other alkyl siloxane derivatives as wellas with vinyl siloxanes and aryl siloxanes (such as phenyl siloxane) andwith mixtures thereof, e.g. with methyl, vinyl, phenyl siloxanes. Asdisclosed in the examples below, dielectric materials having interestingproperties are obtained using about 10 to 50 mole-% of polycyclic alkylsiloxanes, about 30 to 80 mole-% alkyl siloxanes (in particular methylsiloxanes) and the rest, typically about 5 to 30 mole-% vinylsiloxanes/aryl siloxanes.

Thus, in general, the present invention provides novel polymer materialsuseful as low-k materials in dielectric applications, said materialscomprising copolymers formed by copolymerisation of at least onecomonomer having the formula(R³—R⁴)_(n)—Si—(X²)_(4-n),

wherein

-   -   X² is hydrogen or a hydrolysable group selected from halogen,        acyloxy, alkoxy and OH groups,    -   R⁴ is an optional group and comprises an alkylene having 1 to 6        carbon atoms or an arylene and    -   R³ is an alkyl having 1 to 16 carbon atoms, a vinyl having from        2 to 16 carbon atoms, a cycloalkyl having from 3 to 16 carbon        atoms, an aryl having from 5 to 18 carbon atoms or a polycyclic        alkyl group having from 7 to 16 carbon atoms, and    -   n is an integer 1-3,        with at least one of the following silicon compounds:        a) a silicon compound having the general formula III        X³ _(3a)—SiR⁵ _(b)R⁶ _(c)R⁷ _(d)  III        wherein X³ represents a hydrolyzable group; R⁴ is an alkenyl or        alkynyl group, which optionally bears one or more substituents;        R⁵ and R⁶ are independently selected from hydrogen, substituted        or non-substituted alkyl groups, substituted or non-substituted        alkenyl and alkynyl groups, and substituted or non-substituted        aryl groups; a is an integer 0, 1 or 2; b is an integer a+1; c        is an integer 0, 1 or 2; d is an integer 0 or 1; and b+c+d=3; is        hydrolyzed;        b) a silicon compound having the general formula IV        X⁴ _(3e)—SiR⁸ _(f)R⁹ _(g)R¹⁰ _(h)  IV        wherein X⁴ represents a hydrolyzable group; R⁸ is an aryl group,        which optionally bears one or more substituents; R⁹ and R¹⁰ are        independently selected from hydrogen, substituted or        non-substituted alkyl groups, substituted or non-substituted        alkenyl and alkynyl groups, and substituted or non-substituted        aryl groups; e is an integer 0, 1 or 2; f is an integer e+1; g        is an integer 0, 1 or 2; h is an integer 0 or 1; and f+g+h=3;        and        c) a silicon compound having the general formula V        X⁵ _(3-i)—SiR¹¹ _(j)R¹² _(k)R¹³ _(l)  V        wherein X⁵ represents a hydrolyzable group; R¹¹ is a hydrogen or        an alkyl group, which optionally bears one or more substituents;        R¹² and R¹³ are independently selected from hydrogen,        substituted or non-substituted alkyl groups, substituted or        non-substituted alkenyl or alkynyl groups, and substituted or        non-substituted aryl groups; i is an integer 0, 1 or 2; j is an        integer i+1; k is an integer 0, 1 or 2; l is an integer o or 1;        and j+k+l=3,        with the proviso that copolymerization is carried out using at        least one comonomer having the formula II, wherein R₃ is a        polycyclic alkyl group having from 7 to 16 carbon atoms, in        particular 9 to 15 carbon atoms.

Compounds corresponding to the above compounds a) to c) can also bedesignated by the more restricted general formula VI,(R³—R⁴)_(n)—Si—(X²)_(4-n),  VI

wherein

-   -   X² is hydrogen or a hydrolysable group selected from halogen,        acyloxy, alkoxy and OH groups,    -   R⁴ is an optional group and comprises an alkylene having 1 to 6        carbon atoms or an arylene and    -   R³ is an alkyl having 1 to 16 carbon atoms, a vinyl having from        2 to 16 carbon atoms, a cycloalkyl having from 3 to 16 carbon        atoms or an aryl having from 5 to 18 carbon atoms, and    -   n is an integer 1-3.

The alkyl groups of R³ have typically 1 to 6 carbon atoms, the vinylgroups have from 2 to 6 carbon atoms, and the aryl groups have 6 carbonatoms.

The molar ratio between monomeric units derived from compounds accordingto formula II and one or several monomeric unit derived from compoundsof a formula III to VI is in the range of 25:75 to 75:25.

Compounds a) to c) are disclosed in more detail in our copending patentapplication PCT/FI03/00036, the disclosure of which is herewithincorporated by reference.

The present invention also relates to the use of readily hydrolysableadamantyl materials in organo-silsesquioxane polymers for forming low-kdielectrics. Precursors within the scope of the present inventioninclude easily hydrolysable organochlorosilanes or organosilanes thatresult in better polymerization degrees than the similarorgano-alkoxysilanes.

In connection with the invention, we have found that organoalkoxysilaneshave a tendency of leaving residual alkoxides in the material matrix.Such residues greatly impair the use and properties of the materials inparticular as regards their dielectric properties. If residual alkoxidesremain in the matrix, they tend to react over time and change theproperties of materials by forming contaminating alcohol and water intothe matrix. These oxygenates impair dielectric and leakage currentbehavior of the material. In addition, residual alkoxides, such asethoxide-based materials, cause a dangling bond effect that causeshigher leakage current for the material. Moreover, alkoxy-basedmaterials result in higher porosity and lower Young's modulus andhardness compared to well hydrolysable organochloro-silane andorganosilanes. Therefore, the course of the invention is to utilize moreeasily hydrolysable organosilanes for dielectric thin film purposes.

The new polycycloalkyl siloxane precusors used according to theinvention have the general formula I(R¹—R²)_(n)—Si—(X¹)_(4-n),  I

wherein

-   -   each X¹ is independently selected from hydrogen and inorganic        leaving groups,    -   R² is an optional group and comprises alkylene having 1 to 6        carbon atoms or arylene,    -   R¹ is a polycycloalkyl group and    -   n is an integer 1 to 3

By polymerizing a compound of formula I, a polymeric material isobtained which, in practice, is “free of silanols”. This means,typically, that they have a silanol content of less than 0.5 wt-%.

The polymers for preparing the low dielectric constant material have anorganic content of about 30 to 70 wt.-%, preferably higher than 48 wt-%.

The polycyclic alkyl group has from 9 to 16 carbon atoms, and itcomprises preferably a cage compound (as defined above). Typicalexamples of such compounds are adamantyl and diadamantyl. The adamantylor diadamantyl ring structure can be substituted with 1 to 3 alkylsubstitutents, which optionally carry 1 to 6 halogen substitutents, e.g.chloro, fluoro or bromo.

In compounds according to formula I, the inorganic leaving group ispreferably selected from halogens, such as chlorine, bromine orfluorine.

In the compounds according to the above formulas I and II, respectively,

R³ is preferably selected from alkyl groups having 1 to 6 carbon atoms,vinyl groups having from 2 to 6 carbon atoms, and aryl groups having 6carbon atoms;

R¹ or R³, respectively, is directly bonded to the silicon atom; and

R¹ or R³, respectively, is bonded to the silicon atom via an alkylenechain, in particular an alkylene chain selected from methylene, ethyleneand propylene, or an arylene group, in particular phenylene.

As discussed above, compounds of formula I, which are a part of thecompound of formula II, can be copolymerized with other monomers, suchas the monomers of one or several of formulas II to VI.

The molar ratio between monomeric units derived from comonomersaccording to formula I and of formula II, is preferably in the range of25:75 to 75:25.

However, it is also possible to produce polymers useful as dielectric,low-k materials by homopolymerization of compounds of the formula L

The present invention provides novel poly(organosiloxane) materials,which can be hydrolyzed and condensed (alone or with one or more othercompounds) into a hybrid material having a (weight average) molecularweight of from 500 to 100,000 g/mol. The molecular weight can be in thelower end of this range (e.g., from 500 to 5,000 g/mol, or morepreferably 500 to 3,000 g/mol) or the hybrid material can have amolecular weight in the upper end of this range (such as from 5,000 to100,000 g/mol or from 10,000 to 50,000 g/mol). In addition, it may bedesirable to mix a hybrid material having a lower molecular weight witha hybrid material having a higher molecular weight. The hybrid materialcan be suitably deposited such as by spin-on, spray coating, dipcoating, or the like, as will be explained in more detail below.

The present invention also concerns a method of forming a thin filmhaving a dielectric constant of 2.5 or less, comprising

-   -   hydrolyzing a first silicon compound having the formula I        optionally with with a second silicon compound having the        formula II to produce a siloxane material;    -   depositing the siloxane material in the form of a thin layer on        a substrate; and    -   curing the thin layer to form a film.

The present invention further relates to a method of lowering thedielectric constant of the optimized materials in terms of the by rapidthermal curing (RTC). In such a process, the dielectric material iscured (densified and/or crosslinked) by increasing the temperature ofthe material at a rate, which is at least 6 times faster than inconventional curing. As a result, the heating ramp (the time it takes toreach curing temperature) is steep. The actual curing time can also beshorter than conventionally. Typically, the curing time is one sixth ofthe conventional time in the same heating tool. However, the rapid curestep can also be followed by conventional longer cure. The temperaturedifference between the starting temperature and actual the curingtemperature is at least 150° C. At larger temperature differences, lowerdielectric constants are achieved due to changed microstructure of thefilm material. It is not the course of the invention to claim thechanged microstructure, but the changes in the structures due to the RTCtreatment are likely due to phase change between ordered and disorderedmicrostructures in silicon dioxide part of the matrix that results lessdensely packed structure than can be obtained as slightly increasedmicro-porosity. Alternatively, the microstructure changes may also takea place between or within organic residues attached to the silicon oreven between organic residues and silicon dioxide matrix. All thesereactions to cause the microstructure changes may also take a placesimultaneously.

According to a preferred embodiment of the above methods, a non-porousdielectric material is first provided by conventional processing, e.g.by a spin-on or CVD process.

The temperature (also called “the first temperature”) of the typicallypaste-like material is in the range of 100 to 200° C. The material isfree from intentionally incorporated free evaporating porogens in orderto provide a nonporous dielectric material. The elastic modulus of thepaste-like material is low. After the deposition of the material on asuitable support, in particular on a semiconductor substrate, thematerial can optionally be pretreated, as will be explained below inmore detail, and then cured by a thermal curing process, in which thematerial is rapidly heated to an increased (second) temperature.

In the RTC method alternative, the temperature can be increased at anaverage rate of at least 1° C., preferably at least 10° C., inparticular at least 30° C., per second. Thus, a densified nonporousdielectric material having an elastic modulus, which is greater than theelastic modulus of the starting material, can be obtained.

Accordingly, the polymerization and densification reactions of thematerial are activated in a rapid curing furnace so that relativedielectric constant of the dielectric film is lower than a predeterminedvalue. Such a predetermined value corresponds to that of a conventionalfurnace, which means a furnace in which the material is heated at a rateof about 10 deg C. or less per minute and in which it is cured forextensive periods of at least 15 minutes, typically more than 30minutes. By the RTC process, the dielectric constant of the samematerial will be reduced by more than 0.1 as a result of the rapidthermal curing. However, the RTC process can be followed by conventionaltype of heat treatment.

As mentioned above, the temperature difference between the second andthe first temperature should be large, preferably it is at least 200°C., and in particular in the range of from 225 to 425° C., and mostpreferably at least 275° C.

However, it should be pointed out that the present materials can also beprocessed by conventional thermal processing.

The dielectric constant of the densified material is 2.60 or less,preferably 2.50 or less, in particular 2.40 or less. The CTE of the filmis less than 25*10⁻⁶ l/degc.

The material can be characterized as being “nonporous” which, in thepresent context means, in particular, that the porosity is low,typically less than 25%, preferably less than 20%, in particular lessthan 15% (by volume), and the average pore size is less than 5 nm,preferably less than 2 nm and in particular less than 1 nm. As a resultof the processing, the electronic polarizability of the film isdecreased more than 0.1 compared to a predetermined value obtained byconventional processing, as explained above.

As mentioned above, the nonporous dielectric material can be subjectedto annealing or a similar pretreatment or post-treatment of heated tothe second temperature, i.e. the actual curing temperature. Annealing iscarried out, e.g., by a process in which the material is subjected to UVradiation, DUV radiation, Extreme UV radiation, IR radiation or e-beamradiation or a combination thereof. The annealed material is thensubjected to curing at an elevated temperature in air, nitrogen, argon,forming gas or vacuum.

The pre-cure and rapid cure processes according to the presentinvention, result in a dielectric film free of silanols.

The annealed and cured (densified, crosslinked) material can besubjected to deposition of a second layer selected from a metal, abarrier, a liner or an additional dielectric layer.

Based on the above, the present invention provides a process forpreparing a siloxane-based dielectric material on a semiconductorsubstrate by hydrolysis and condensation of corresponding reactants,applying the prepared compositions on a substrate in the form of a thinlayer, patterning the film by selective radiation and developing theradiated film and curing the formed structure.

As an embodiment of the above process, the material above is processedfirst by introducing a monomeric or polymerized material on asemiconductor substrate by a spin-on or CVD method, and then forming asiloxane polymer film on the semiconductor substrate by activatingpolymerization and densification reactions by rapid curing processing soas to produce a material having a relative dielectric constant lowerthan 2.6, preferably less than 2.5, in particular less than 2.4.Typically the dielectric constant is between 2.0 and <2.6.

The pore size of the nonporous dielectric material is less than 2 nm,the co-efficient of thermal expansion less than 25 ppm/degC., and thethermal decomposition temperature higher than 450° C.

The electrically insulating material can be baked and patterned, with anelectrically conductive material being deposited in removed areas of thepatterned dielectric. The electrically conductive material comprises,for example, copper.

The above process is, e.g., a dual damascene process.

The deposition and patterning processes are described, for instance, inour earlier application PCT/FI03/00036, the disclosure of which isherewith incorporated by reference.

The following non-limiting examples illustrate the invention:

EXAMPLE 1

Precursor Material

Adamantyltrichlorosilane C₁₀H₁₅SiCl₃

Preparation Steps:

1. C₁₀H₁₆+2Br₂→1,3-C₁₀H₁₄Br₂+2 HBr

2. 1,3-C₁₀H₁₄Br₂+2 Li→C₁₀H₁₄+2LiBr

3. C₁₀H₁₄+HSiCl₃ →C ₁₀H₁₅SiCl₃

106.4 g of (0.781 mol) adamantane C₁₀H₁₆ was added to a 2000 ml vesselfollowed by 500 ml dichloromethane. The solution was heated up to 40° C.and 92 ml (286.95 g, 1.80 mol) bromine was added to the vessel followedby a small amount of FeBr₃ as catalyst. The solution was stirred at 40°C. for 15 hours.

Refluxing was stopped and solution washed with 500 ml of dilute HCl. Asodium thiosulfate solution was added to the vessel until the colourchanged from red to brown. The organic layer was separated andevaporated to dryness. Crude 1,3-C₁₀H₁₄Br₂ was dissolved in hot n-hexaneand filtered. The filtrate was placed in a refrigerator andcrystallized; the obtained, purified 1,3-C₁₀H₁₄Br₂

was filtered and dried in vacuum. Yield 192 g (84%).

58 g metallic lithium was added to a 2000 ml vessel followed by 500 mlEt₂O. 192 g (0.656 mol) adamantyl dibromide was dissolved in 1000 mlEt₂O and the solution was added to the Li/Et₂O solution at roomtemperature during an hour. The obtained solution was stirred for 15hours at room temperature.

Then, the solution was decanted and Et₂O evaporated. Adamantyl dehydratewas extracted from the remaining solid material by 3×200 ml n-pentane.n-pentane was evaporated. The remaining 1,3-dehydroadamantane

was used without further purification.

It was placed in a 1000 ml vessel and followed by 600 ml HSiCl₃ and 100μl Speier's catalyst (H₂PtCl₆ in alcohol). The solution was heated up to40° C. for two hours. After that, excess HSiCl₃ was distilled off andthe remaining C₁₀H₁₅SiCl₃

was purified by distillation. B.p. 95° C./1 mbar. Yield 123 g.

Adamantylsilane, an optional precursor, was manufactured as a derivativeof adamantyl trichlorosilane.

Lithium aluminum hydride (6.18 g) and dry ether (80 mL) were placed in arb flask. Adamantyl trichlorosilane (50.8 g), dissolved in ether (50 mL)was added dropwise in the magnetically stirred flask at rt. The reactionwas allowed to reflux for 24 h. The solution was filtered, evaporated,and 1 mL Et₃N in 30 mL pentane was then added and the upper layer wascarefully decanted. After evaporation, the crude reaction product wasdistilled, giving 22 g of adamantylsilane (70%, bp. 40 . . . 50° C./2mbar). ¹H NMR: 1.95 (15H), 3.68 (3H). ¹³C NMR: 20.63, 28.86, 37.99,40.61. ²⁹Si NMR: —43.55 (q, Si—H: 190 Hz). Purity was found to be 95.7%by GC.

Adamantylchlorosilylbis(dimethylamine), another optional precursor, wasmanufactured as a derivative of adamantyl trichlorosilane.

Adamantyltrichlorosilane (5.59 g), Et₃N (9.5 g) and dry ether (40 mL)were placed in a rb flask. Dimethylamine (3.05 g) was slowly bubbledinto the solution at 0° C. in 45 minutes. The reaction was allowed tostir for 18 hours at rt. It was then filtered, and volatiles wereRemoved by vacuum. Distillation at 88 . . . 98° C./1 mbar gave afraction 4.54 g (76%). Purity was 97% by GC. GC/MS (m/z): 296 (62,[M]⁺), 243 (42), 151 (100), 135 (43), 108 (33), 79 (17), 74 (37). ¹HNMR: 1.99 (3H), 2.08 (6H), 2.19 (6H), 2.74 (12H). ¹³C NMR 28.63, 38.29,39.07, 48.68.14N NMR: −373.9. 29Si NMR: −10.16.

Other applicable precursors include (but are not limited to) thefollowing: (#2)

Adamantyl trichlorosilane (#3)

3,5,7-trifluoroadamantyl trichlorosilane (#4)

3,5,7-trifluoromethylada- mantyl trichlorosilane (#5)

Adamantylphenyl trichloro- silane

In addition, an interesting precursor compound is formed byadamantylpropyl trichlorosilane.

EXAMPLE 2

Polymer Preparation

Material 1

Preparation of adamantysilanol intermediate. 7.0 g ofadamantyltrichlorosilane (0.02595 mol) was dissolved in 56 ml acetone.The solution was transferred drop by drop into a solution containingacetone (70 ml), triethylamine (9.19 g, 0.0908 mol) and water (4.67 g,0.2595 mol) within 20 min. During addition, the solution was vigorouslymixed and the temperature of solution was maintained at room temperature(20° C., water bath). White precipitate was formed. After addition, thesolution was mixed for an additional 20 hours at room temperature.

The solution was dried to dryness with a rotary evaporator (30° C., 200mbar). 50 ml water was added and stirred for 10 min. After this, thesolution was filtrated and the white powder obtained was flushed threetimes with 25 ml of water. The powder was dried under vacuum (40° C., 1mbar), whereby 5.14 g of adamantylsilanol material was obtained thatcontained monomeric and oligomeric compounds.

Preparation of low-k resin. 5.0 g of adamantylsilanol was dissolved in17.4 ml N,N-dimethylacetamide (DMAc) at 65° C. and the solution wascooled to room temperature. The solution was transferred drop by dropinto a solution containing methyltrichlorosilane (15.8 g, 0.106 mol),vinyltrichlorosilane (2.0 g, 0.0123 mol), diethyl ether (77 ml), andtriethylamine (8.7 g, 0.0867 mol) within 15 min. During addition, thesolution was vigorously mixed and the temperature of the solution wasmaintained at room temperature (20° C., water bath). After addition, thesolution was mixed for 1 hour at room temperature.

The obtained solution was dried to dryness under vacuum (40° C., 1 mbar,30 min). 77 ml of dichloromethane (CM) was then added and the solutionwas placed in ice bath. 22 ml of hydrochloric acid (37%) was added dropby drop within 30 min. After that, the reaction mixture was stirred for90 min at a temperature below 5° C. and at room temperature for 60 min.

The DCM phase was allowed to separate and was removed. HCl/water phasewashed two times with 30 ml of DCM. DCM solutions were combined andextracted 8 times with 500 ml of water (pH 6). The combined DCM solutionthus obtained was dried into dryness with a rotary evaporator (40° C.,10 mbar, 45 min) and finally at high vacuum (20° C., 1 mbar, 2 h). 6.0 gof material was obtained. Molecular weight (M_(p)) of the material was17900 g/mol, determined by gel permeation chromatography (GPC) againstcommercially available narrow polystyrene standards

The polymeric material was dissolved in 140 ml toluene containing 1 wt.% triethylamine. The solution was refluxed for 2 hours and then dried todryness with a rotary evaporator (60° C., 10 mbar, 40 min) and finallywith high vacuum (20° C., 1 mbar, 2 h). 5.78 g of material was obtained.Molecular weight (M_(p)) was 26 080 g/mol measured by GPC. ^(t)H NMRshowed the composition being 23 mole-% for adamantyl, 66 mole-% formethyl, and 11 mole-% for vinyl repeating units. To was 460° C. andweight loss between 400-500° C. (heating rate 5° C./min) was 2.7%measured by thermal gravimetric analysis (TGA).

EXAMPLE 3

Polymer Material 1A—Alternative Method

Preparation of adamantylsilanol intermediate. Preparation ofadamantylsilanol was made similarly as in Example 2, but tetrahydrofuran(THF) was used instead of acetone. Thus, 7.0 g ofadamantyltrichlorosilane (0.02595 mol) was dissolved in 21 ml THF. Thesolution was transferred drop by drop into a solution containing THF (70ml), triethylamine (9.19 g, 0.0908 mol), and water (4.6 μg, 0.2595 mol)within 20 min. During addition, the solution was vigorously mixed andthe temperature of the solution was maintained at room temperature (20°C., water bath). White precipitate was formed. After addition, thesolution was mixed for a further 22 hours at room temperature.

The solution was dried to dryness with a rotary evaporator (35° C., 170mbar). 50 ml water was added and stirred for 10 min. After this, thesolution was filtrated and the obtained white powder was flushed threetimes with 25 ml of water. The powder was dried under vacuum (40° C., 1mbar). 4.62 g of adamantylsilanol material was obtained that containedmonomeric and oligomeric compounds.

EXAMPLE 4

Polymer Material 1B—Alternative Method

9.75 g of adamantylsilanol prepared in Example 1 was dissolved in 34 mlN,N-dimethylacetamide (DMAc) at 65° C., and the solution was cooled toroom temperature. The solution was transferred drop by drop into asolution containing methyltrichlorosilane (30.1 g, 0.201 mol),vinyltrichlorosilane (4.3 g, 0.026 mol), diethyl ether (146 ml), andtriethylamine (16.6 g, 0.164 mol) within 30 min. During addition, thesolution was vigorously mixed and the temperature of the solution wasmaintained at room temperature (20° C., water bath). After addition, thesolution was mixed for a further 3 hours at room temperature.

The solution was dried into dryness under vacuum (40° C., 1 mbar, 2 h).150 ml of dichloromethane (DCM) was added and the solution thus obtainedwas placed in ice bath. 36 ml of hydrochloric acid (37%) was added dropby drop within 60 min. After the addition of the hydrochloric acid, thereaction mixture was stirred for 90 min below 5° C. and for 24 h at roomtemperature.

The DCM phase was allowed to separate and was collected. HCl/water phasewashed two times with 60 ml of DCM. The DCM solutions were combined andextracted with 10 times with 200 ml of water (pH 6). The combined DCMsolution was dried to dryness with a rotary evaporator (40° C., 10 mbar,60 min) and finally under vacuum (20° C., 1 mbar, 60 min). 11.6 g ofmaterial was obtained. Molecular weight (M_(p)) was 27 610 g/molmeasured by gel permeation chromatography (GPC).

The material was dissolved in 232 ml toluene containing 1 wt. %triethylamine. The solution was refluxed (oil bath temperature 150° C.)for 2 hours and then dried to dryness with a rotary evaporator (60° C.,10 mbar, 60 min) and finally with high vacuum (20° C., 1 mbar, 2 h).11.8 g of material was obtained. Molecular weight (M_(p)) was 30 500g/mol, measured by GPC. ¹H NMR showed the composition being 27 mole-%for adamantyl, 62 mole-% for methyl, and 11 mole-% for vinyl repeatingunits. T₀ was 460° C. and weight loss between 400-500° C. (at a heatingrate of 5° C./min), was 3.2% measured by thermal gravimetric analysis(TGA).

EXAMPLE 5

Polymer Material 1C—Alternative Method

3.6 g of low molecular weight material prepared in Example 3 wasdissolved in 18 ml xylene containing 4 wt. % triethylamine. The solutionwas refluxed for 3 hours. Then, it was dried to dryness with a rotaryevaporator (70° C., 10 mbar, 30 min) and finally with high vacuum (70°C., 1 mbar, 2 h). 3.45 g of material was obtained. The molecular weight(M_(p)) was 46 880 g/mol, measured by GPC.

EXAMPLE 6

Comparative Material 2B

A comparative material 2B was prepared having a similar compositionalstructure as polymer material 1B, but using organotrialkoxysilanes asprecursors instead of the corresponding trichlorosilanes of Example 4.Thus, adamantyltriethoxysilanesilane, methyltriethoxysilane, andvinyltriethoxysilane were used in ratios that yielded similar finalcompositional concentrations of organo-functional moieties in the finalpolymer as presented in Example 4 for Polymer Material 1B. Theprecursors were dissolved in acetone and the solution thus obtained wasplaced in ice bath and 9.52 g of 0.5 M hydrochloric acid was added dropby drop within 50 min. During addition, the solution was vigorouslystirred. After the addition, the solution was refluxed for another 3hours. An excess amount of toluene was added and acetone was evaporated.An excess amount of water was added and the solution was allowed to stirfor 10 minutes at room temperature. The toluene phase was allowed toseparate and was removed. The solution was dried to dryness with arotary evaporator and, finally, with high vacuum.

Material was dissolved in an extensive amount of toluene containing 1wt. % triethylamine. The solution was refluxed for 1 hour, dried todryness with rotary evaporator and finally with high vacuum. Ahomogenous polymer with yield of 65% was obtained. Molecular weight(M_(p)) was 21 840 g/mol measured by GPC.

EXAMPLE 7

Processing and Testing of Example Materials

Test Film IA

A test film was prepared from material 1B disclosed in Example 4 usingspin-on deposition by applying 3000 rpm spinning speed and resulting in500 nm thick film. The film was deposited on a n-type silicon wafer andpre-cured on a hot-plate for 5 minutes at 200° C. prior to final in afurnace treatment. The furnace anneal was done under nitrogen gas flowat 450° C. for 60 minutes. Dielectric constants were measured fromMOS-capacitor (metal-insulator-semiconductor structure) type device.Applied measurement frequency was 100 kHz. Porosity was measured withporosity ellipsometer and Young's modulus and hardness bynanoindentation.

Test Film IB

A test film was prepared from material 1B explained in Example 4 byspin-on deposition by applying a 3000 rpm spinning speed and resultingin a 500 nm thick film. The film was deposited on an n-type siliconwafer and pre-cured on a hot-plate for 5 minutes at 200° C. prior tofinal treatment by rapid thermal anneal treatment. The rapid thermalanneal was done under vacuum at 450° C. for 5 minutes and a 30°C./second temperature ramp rate was utilized. Dielectric constants weremeasured from a MOS-capacitor (metal-insulator-semiconductor structure)type device. The applied measurement frequency was 100 kHz. Porosity wasmeasured with porosity ellipsometer and Young's modulus and hardness bynanoindentation.

Test Film IIK

A test film was prepared from material 2B explained in Example 6 byspin-on deposition by applying a 3000 rpm spinning speed and resultingin a 500 nm thick film. The film was deposited on an n-type siliconwafer and pre-cured on a hot-plate for 5 minutes at 200° C. prior tofinal curing by furnace treatment. The furnace anneal was done undernitrogen gas flow at 450° C. for 60 minutes. Dielectric constants weremeasured from a MOS-capacitor (metal-insulator-semiconductor structure)type device. The applied measurement frequency was 100 kHz. Porosity wasmeasured with porosity ellipsometer and Young's modulus and hardness bynanoindentation.

Test Film IIB

A test film was prepared from material 2B explained in Example 6 byspin-on deposition by applying a 3000 rpm spinning speed and resultingin a 500 nm thick film. The film was deposited on an n-type siliconwafer and pre-cured on a hot-plate for 5 minutes at 200° C. prior tofinal curing by rapid thermal anneal treatment. The rapid thermal annealwas done under vacuum at 450° C. for 5 minutes and a 30° C./secondtemperature ramp rate was utilized. Dielectric constants were measuredfrom a MOS-capacitor (metal-insulator-semiconductor structure) typedevice. The applied measurement frequency was 100 kHz. Porosity wasmeasured with porosity ellipsometer and Young's modulus and hardness bynanoindentation.

The results of the tested films are summarized in Table 2: TABLE 2Dielectric Young's Leakage constant Porosity modulus Hardness currentFilm (10 kHz) % Gpa) (GPa) (nA/cm2) I.A. 2.53 8 6.9 0.52 0.03 I.B. 2.3217 6.5 0.49 0.05 II.A. 2.62 13 6.4 0.32 0.7 II.B. 2.42 28 3.8 0.19 1.2

Clearly, based on the comparative data, it is advantageous to useorgano-chlorosilanes and their derivatives as starting materials orprecursors since they result in better electrical properties, such aslower dielectric constant, with lower porosity as well as bettermechanical performance. The residual silanol levels are also lower inthe case of using organo-chlorosilanes as precursors than can beobserved as significantly lower leakage current in actual testeddevices. The better overall performance of organo-chlorosilanes derivesfrom the fact that they are easily hydrolysed and polycondensed and,thus, results in purer polymer network that is free of silanol typeimpurities.

1. A low dielectric constant polymer, comprising monomeric units derived from a compound having the general formula I (R¹—R²)_(n)—Si—(X¹)_(4-n),  I wherein each X¹ is independently selected from hydrogen and inorganic leaving groups, R² is an optional group and comprises an alkylene having 1 to 6 carbon atoms or an arylene, R¹ is a polycycloalkyl group and n is an integer 1 to 3
 2. The polymer according to claim 1, wherein the organic content of the polymer is in the range of 30 to 70 wt.-%, preferably higher than 48 wt-%.
 3. The polymer according to claim 1, wherein R¹ is a polycyclic alkyl group having from 9 to 16 carbon atoms.
 4. The polymer according to claim 3, wherein R¹ is a cage compound.
 5. The polymer according to claim 4, wherein R¹ is adamantyl or diadamantyl.
 6. The polymer according to claim 5, wherein the adamantyl or diadamantyl is substituted with 1 to 3 alkyl substitutents, which optionally carry 1 to 6 halogen substituents.
 7. The polymer according to claim 1, wherein the inorganic leaving group is selected from halogens.
 8. The polymer according to claim 1, obtainable by homopolymerization of compounds of the formula I.
 9. The polymer according to claim 1, which is obtainable by copolymerization of a compound of formula I with a compound of formula II (R³—R⁴)_(n)—Si—(X²)_(4-n),  II wherein X² is hydrogen or a hydrolysable group selected from halogen, acyloxy, alkoxy and OH groups, R⁴ is an optional group and comprises an alkylene having 1 to 6 carbon atoms or an arylene and R³ is an alkyl having 1 to 16 carbon atoms, a vinyl having from 2 to 16 carbon atoms, a cycloalkyl having from 3 to 16 carbon atoms, an aryl having from 5 to 18 carbon atoms or a polycyclic alkyl group having from 7 to 16 carbon atoms, and n is an integer 1-3.
 10. The polymer according to claim 9, wherein R³ is selected from alkyl groups having 1 to 6 carbon atoms, vinyl groups having from 2 to 6 carbon atoms, and aryl groups having 6 carbon atoms.
 11. The polymer according to claim 9, wherein the molar ratio between monomeric units derived from compounds according to formula I and of formula II is in the range of 25:75 to 75:25.
 12. The polymer according to claim 9, wherein R¹ or R³, respectively, is directly bonded to the silicon atom.
 13. The polymer according to claim 9, wherein R¹ or R³, respectively, is bonded to the silicon atom via an alkylene chain selected from methylene, ethylene and propylene, or an arylene group selected from phenylene.
 14. The polymer according the claim 1, wherein the total sum dielectric components at 1 MHz is 2.50 or less, preferably 2.1 or less.
 15. The polymer according to claim 14, wherein the orientational dielectric constant of the polymer is 0.4 or less.
 16. The polymer according to claim 1, wherein the oxygen content of the polymer is less than 15 atomic %.
 17. The polymer according to claim 9, wherein the carbon content of the polymer is more than 25 atomic %.
 18. The polymer according to claim 1, wherein the dielectric constant of the dielectric material after curing is 2.50 or less, preferably 2.30 or less.
 19. The polymer according to claim 1, wherein the porosity of the dielectric material is less than 20%, preferably less than 15%.
 20. The polymer according to claim 1, wherein the average pore radius is less than 1 nm.
 21. The polymer according to claim 1, wherein the Young's modulus of the film is higher than 4 GPa after curing, in particular higher than 6 GPa.
 22. A low dielectric constant polymer, comprising monomeric units derived from a compound selected from the group consisting of adamantyl trichlorosilane, adamantylpropyl trichlorosilane, 3,5,7-trifluoroadamantyl trichlorosilane, 3,5,7-trifluoromethyladamantyl trichlorosilane and adamantylphenyl trichlorosilane.
 23. A method of forming a thin film having a dielectric constant of 2.5 or less, comprising hydrolyzing a first silicon compound having the formula I optionally with at least one second silicon compound having the formula II to produce a siloxane material; depositing the siloxane material in the form of a thin layer on a substrate; and curing the thin layer to form a film. 24-45. (canceled)
 46. Composite material useful as low-k materials in dielectric applications, said materials comprising copolymers formed by copolymerisation of at least one comonomer having the formula (R³—R⁴)_(n)—Si—(X²)_(4-n),  II wherein X² is hydrogen or a hydrolysable group selected from halogen, acyloxy, alkoxy and OH groups, R⁴ is an optional group and comprises an alkylene having 1 to 6 carbon atoms or an arylene and R³ is an alkyl having 1 to 16 carbon atoms, a vinyl having from 2 to 16 carbon atoms, a cycloalkyl having from 3 to 16 carbon atoms, an aryl having from 5 to 18 carbon atoms or a polycyclic alkyl group having from 7 to 16 carbon atoms, and n is an integer 1-3, with a silicon compound selected from the group of a) silicon compounds having the general formula III X³ _(3-a)—SiR⁵ _(b)R⁶ _(c)R⁷ _(d)  III wherein X³ represents a hydrolyzable group; R⁴ is an alkenyl or alkynyl group, which optionally bears one or more substituents; R⁵ and R⁶ are independently selected from hydrogen, substituted or non-substituted alkyl groups, substituted or non-substituted alkenyl and alkynyl groups, and substituted or non-substituted aryl groups; a is an integer 0, 1 or 2; b is an integer a+1; c is an integer 0, 1 or 2; d is an integer 0 or 1; and b+c+d=3; is hydrolyzed; b) silicon compound having the general formula IV X⁴ _(3-e)—SiR⁸ _(f)R⁹ _(g)R¹⁰ _(h)  IV wherein X⁴ represents a hydrolyzable group; R⁸ is an aryl group, which optionally bears one or more substituents; R⁹ and R¹⁰ are independently selected from hydrogen, substituted or non-substituted alkyl groups, substituted or non-substituted alkenyl and alkynyl groups, and substituted or non-substituted aryl groups; e is an integer 0, 1 or 2; f is an integer e+1; g is an integer 0, 1 or 2; h is an integer 0 or 1; and f+g+h=3; and c) silicon compounds having the general formula V X⁵ _(3-i)—SiR¹¹ _(j)R¹² _(k)R¹³ _(l)  V wherein X⁵ represents a hydrolyzable group; R¹¹ is a hydrogen or an alkyl group, which optionally bears one or more substituents; R¹² and R¹³ are independently selected from hydrogen, substituted or non-substituted alkyl groups, substituted or non-substituted alkenyl or alkynyl groups, and substituted or non-substituted aryl groups; i is an integer 0, 1 or 2; j is an integer i+1; k is an integer 0, 1 or 2; l is an integer 0 or 1; and j+k+l=3, with the proviso that copolymerisation is carried out using at least one comonomer having the formula II, wherein R₃ is polycyclic alkyl group having from 7 to 16 carbon atoms.
 47. (canceled)
 48. A method for forming a dielectric material having a dielectric constant of 2.6 or less, on a semiconductor substrate, comprising the steps of: introducing a monomeric, oligomeric or fully or partially polymerized deposition material on a semiconductor substrate by a spin-on or CVD method, said deposition material formed from a precursor material comprising a silicon-containing chemical compound having the formula I as defined in claim 1; forming a siloxane polymer film from the deposition material on the semiconductor substrate by activating polymerization and densification reactions by a curing process; and thereby forming a material on the semiconductor substrate having a relative dielectric constant lower than 2.6. 49-53. (canceled) 